Fabric for air-bag, using polyethylene terephthalate with excellent heat resistance

ABSTRACT

Provided is a fabric for an airbag using a polyethylene terephthalate fiber, and particularly, to a fabric for an airbag having enhanced thermal resistance and instantaneous thermal strain rate, which is manufactured using a polyethylene terephthalate fiber for an airbag manufactured by controlling the strength and elongation of the polyethylene terephthalate fiber to replace a conventional fabric for an airbag using a yarn formed of nylon 66. The fabric for an airbag including a polyethylene terephthalate fiber manufactured by spinning a polyethylene terephthalate chip having an intrinsic viscosity of 0.8 to 1.3 dl/g has thermal resistances of 0.45 to 0.65 seconds at 450° C., and 0.75 to 1.0 seconds at 350° C.

TECHNICAL FIELD

The present invention relates to a fabric for an airbag using apolyethylene terephthalate fiber, and particularly, to a fabric for anairbag having enhanced thermal resistance and instantaneous thermalstrain rate, which is manufactured using a polyethylene terephthalatefiber for an airbag manufactured by controlling the strength andelongation of the polyethylene terephthalate fiber to replace aconventional fabric for an airbag using a yarn formed of nylon 66.

BACKGROUND ART

An airbag requires characteristics of low air permeability to easilyrupture in a car crash, and energy absorbability to prevent damage toand bursting of the airbag itself. In addition, to be more easilystored, characteristics relating to foldability of a fabric itself arerequired. As a suitable fiber having the above-describedcharacteristics, nylon 66 has generally been used. However, recently, inorder to save on cost, attention on fibers other than nylon 66 has beenincreasing.

As a fiber capable of being used for an airbag, polyethyleneterephthalate may be used. However, when polyethylene terephthalate isused as a yarn for an airbag, seams rupture during airbag cushion moduletests. To solve this problem, it is important to use a polyethyleneterephthalate yarn that does not degrade the energy absorbability of anairbag. In addition, it is necessary to improve flexibility of thefabric for an airbag using a polyethylene terephthalate fiber to beeasily stored.

DISCLOSURE Technical Problem

The present invention is directed to providing a fabric for an airbagusing polyethylene terephthalate, which has excellent energyabsorbability resulting in fewer ruptures of outer seams during anairbag cushion development tests, and is more easily stored.

Technical Solution

According to an exemplary embodiment of the present invention, a fabricfor an airbag including a polyethylene terephthalate fiber manufacturedby spinning a polyethylene terephthalate chip having an intrinsicviscosity of 0.8 to 1.3 dl/g is provided. The fabric for an airbag has athermal resistance of 0.45 to 0.65 seconds at 350° C., which iscalculated by the following Equation.

Thermal Resistance (sec) of Fabric=T ₁ −T ₂  [Equation 1]

In Equation 1, T₁ is the time in which a steel rod heated to 350° C.falls from 10 cm above the fabric through the fabric, and T₂ is the timein which the same steel rod falls from the same height.

According to another exemplary embodiment of the present invention, afabric for an airbag including a polyethylene terephthalate fibermanufactured by spinning a polyethylene terephthalate chip having anintrinsic viscosity of 0.8 to 1.3 dl/g is provided. The fabric for anairbag has a thermal resistance of 0.75 to 1.0 seconds at 450° C., whichis calculated by the following Equation, and an instantaneous thermalstrain rate of 1.0 to 5.0%.

Thermal Resistance (sec) of Fabric=T ₃ −T ₄  [Equation 2]

In Equation 2, T₃ is the time that a steel rod heated to 450° C. fallsfrom 10 cm above the fabric through the fabric, and T₄ is the time thatthe same steel rod falls from the same height.

According to still another exemplary embodiment of the presentinvention, the fabric for an airbag has a stiffness of 5.0 to 15.0 N.

According to yet another exemplary embodiment of the present invention,the polyethylene terephthalate fiber has a strength of 8.0 to 11.0 g/d,and an elongation of 15 to 30% at room temperature.

According to yet another exemplary embodiment of the present invention,the polyethylene terephthalate fiber has an instantaneous thermal strainrate of 1.0 to 5.0%, and a filament size of 4.5 deniers or less.

Advantageous Effects

The present invention provides a polyethylene terephthalate fabric foran airbag, which overcomes the lack of flexibility, which is adisadvantage of a conventional fabric for an airbag, and has betterthermal resistance. As a result, an airbag module manufactured using thefabric for an airbag can be more easily stored and rarely bursts due topressure and heat instantaneously applied by a high temperatureexpanding gas during airbag development tests.

BEST MODE

The present invention provides a polyethylene terephthalate fabric foran airbag manufactured by manufacturing a polyethylene terephthalatefiber for an airbag by controlling the strength and elongation of thepolyethylene terephthalate fiber, thereby obtaining excellent thermalresistance and instantaneous thermal strain rate. Accordingly, outerseams rupture less frequently during airbag cushion development tests,and the foldability and storability of the fabric for an airbag areimproved.

In the present invention, the fabric for an airbag uses a polyethyleneterephthalate multifilament obtained by spinning a polyethyleneterephthalate chip having an intrinsic viscosity (IV) of 0.8 to 1.3 dl/gto safely absorb instantaneous impact energy of an exhausted gasgenerated due to explosion of gunpowder in the airbag. A polyester yarnhaving an intrinsic viscosity (IV) of less than 0.8 dl/g is not suitablebecause the polyester yarn does not have sufficient toughness to be usedas an airbag.

A resin for producing a synthetic fiber multifilament for an airbag maybe selected from the group consisting of polymers such as polyethyleneterephthalate, polybutylene terephthalate, polyethylene naphthalate,polybutylene naphthalate,polyethylene-1,2-bis(phenoxy)ethane-4,4′-dicarboxylate, andpoly(1,4-cyclohexylene-dimethylene terephthalate); copolymers includingat least one of the polymers as a repeated unit, such as polyethyleneterephthalate/isophthalate copolyester, polybutyleneterephthalate/naphthalate copolyester, and polybutyleneterephthalate/decane dicarboxylate copolyester; and a mixture of atleast two of the polymers and copolymers. Among these, in the presentinvention, a polyethylene terephthalate resin is most preferably used interms of mechanical properties and the formation of a fiber.

The polyethylene terephthalate fiber for an airbag of the presentinvention may have a strength of 8.0 to 11.0 g/d and an elongation of 15to 30% at room temperature. When a strength of the polyethyleneterephthalate fiber for an airbag of the present invention is less than8.0 g/d, the polyethylene terephthalate fiber is not suitable for thepresent invention because of low tensile and tearing strengths of themanufactured fabric for an airbag.

In addition, when the elongation of the fiber is less than 15%, energyabsorbability is decreased when an airbag cushion is suddenly expanded,and thus the airbag cushion bursts, which is not suitable. When a yarnis manufactured to have the elongation of the fiber of more than 30%,sufficient expression of the strength is difficult due to thecharacteristics of a process of manufacturing a yarn.

The polyethylene terephthalate fiber for an airbag of the presentinvention may have a filament size of 4.5 deniers or less, andpreferably 3 deniers or less. Generally, as a fiber having a smallerfilament size is used, the obtained fabric becomes flexible, therebyachieving excellent foldability and better storability. In addition,when the filament size is smaller, covering properties are enhanced atthe same time. As a result, air permeability of the fabric may beinhibited. When the filament size is more than 4.5 deniers, the fabrichas degraded foldability and storability, and low air permeability, andthus the fabric cannot properly serve as a fabric for an airbag.

The polyethylene terephthalate fiber for an airbag of the presentinvention may have an instantaneous thermal strain rate of 0.1 to 5.0%,and preferably 2.0 to 4.0% at 100° C. When the instantaneous thermalstrain rate of the fiber is less than 1.0%, the absorbability of energyapplied when the airbag cushion is expanded due to a high temperaturegas is degraded, and thus the airbag cushion bursts easily. In addition,when the instantaneous thermal strain rate of the fiber is more than5.0%, a length of the fiber is increased at high temperature, and thusseams of the airbag cushion rupture when it is expanded due to a hightemperature gas. Therefore, an uncontrolled expanding gas is leaked.

In the uncoated polyethylene terephthalate fabric whose density is 50wefts or warps per inch after a scouring and contracting process,stiffness may be approximately 5.0 to 15.0 N, and preferably 6.0 to 9.0N when evaluated by circular bend measurement. When the stiffness ismore than 15.0 N, the fabric becomes stiff, and thus is difficult tostore in the manufacture of the airbag module and degraded in developingperformance of the airbag cushion.

In the uncoated polyethylene terephthalate fabric whose density is 50wefts or warps per inch after a scouring and contracting process,thermal resistance measured using a rod heated at 350° C. in a hot rodtest may be 0.75 to 1.0 seconds. When the thermal resistance measured at350° C. is less than 0.75 seconds, the thermal resistance of the fabricfor an airbag is too low to withstand a high temperature gas in thedevelopment of the airbag cushion, and thus outer seams of the airbageasily rupture. When the thermal resistance measured at 350° C. is morethan 1.0 second, since a polyethylene terephthalate yarn having a largerfilament size is necessarily used, the stiffness of the fabric isincreased, and thus the fabric for an airbag is difficult to store inthe module.

In the uncoated polyethylene terephthalate fabric whose density is 50wefts or warps per inch after a scouring and contracting process,thermal resistance measured using a steel rod heated to 450° C. in a hotrod test may be 0.45 to 0.65 seconds. When the thermal resistancemeasured at 450° C. is less than 0.45 seconds, the thermal resistance ofthe fabric for an airbag is too low to withstand a high temperature gasin the development of the airbag cushion, and thus outer seams of theairbag easily rupture. When the thermal resistance measured at 450° C.is more than 0.65 seconds, since a polyethylene terephthalate yarnhaving a larger filament size is necessarily used, the stiffness of thefabric is increased, and thus the fabric for an airbag is difficult tostore in the module.

In the present invention, the fabric may be woven with the polyethyleneterephthalate fiber as a plain fabric having a symmetrical structure.Alternately, to obtain more favorable physical properties, the fabricmay be woven as a 2/2 panama fabric having a symmetrical structure usinga yarn having a smaller linear density.

The woven fabric may be coated with a coating agent selected ofsilicon-, polyurethane-, acryl-, neoprene-, and chloroprene-basedcoating agents at a weight of 15 to 60 g/m² to secure low airpermeability, which is suitable for the fabric for an airbag.

Evaluation of physical properties in Examples and Comparative Exampleswere performed as follows:

1) Intrinsic Viscosity (I.V.)

0.1 g of a sample was dissolved in a reagent prepared by mixing phenoland 1,1,2,2-tetrachloroethanol in a weight ratio of 6:4 (90° C.) for 90minutes. The resulting solution was transferred to an Ubbelohdeviscometer and maintained in a constant temperature oven at 30° C. for10 minutes, and a drop time of the solution was measured using aviscometer and an aspirator. A drop time of a solvent was also measuredas described above, and then R.V. and I.V. values were calculated by thefollowing equations.

R.V.=Drop Time of Sample/Drop Time of Solvent

I.V.=1/4×[(R.V.−1)/C]+3/4×(In R.V./C)

In the above equation, C is the concentration (g/100 ml) of the samplein the solution.

2) Measurement of Instantaneous Thermal Strain Rate

A bundle of filaments having a thickness of approximately 59 deniers wasmade by randomly selecting filaments from a multi filament yarn. Thebundle of filaments was mounted on a TA instrument (model name: TMSQ-400) to have a length of 10 mm, and then a stress of 1.0 gf/den wasapplied thereto. 2 minutes after the application of a stress, a teststarted and a temperature was rapidly increased from 30 to 100° C. for30 minutes. An instantaneous thermal strain rate was obtained bydividing a length increment of the sample when the temperatureapproached 100° C. by an initial length of the sample, and is shown as apercentage.

3) Measurement of Stiffness of Fabric

The stiffness of a fabric was measured by circular bend measurementaccording to the specification of ASTM D4032. Here, the stiffness wasmeasured with respect to weft and warp directions, and an average of thevalues obtained in the weft and warp directions is shown in units ofNewtons (N).

4) Method of Measuring Thermal Resistance of Fabric (350° C. Hot RodTest)

A cylindrical steel rod having a weight of 50 g and a diameter of 10 mmwas heated to 350° C. and then dropped vertically from 10 cm above afabric for an airbag. Here, the time in which the heated rod fellthrough the fabric was T₁, and the time in which the rod fell withoutthe fabric was T₂. The thermal resistance was measured by the followingequation. Here, one layer of the unfolded fabric for an airbag was used.

Thermal Resistance (Sec.) of Fabric=T ₁ −T ₂  [Equation 1]

5) Method of Measuring Thermal Resistance of Fabric (450° C. Hot RodTest)

A cylindrical steel rod having a weight of 50 g and a diameter of 10 mmwas heated to 450° C. and then dropped vertically from 10 cm above afabric for an airbag. Here, the time in which the heated rod fellthrough the fabric was T₃, and the time in which the rod fell withoutthe fabric was T₄. The thermal resistance was measured by the followingequation. Here, one layer of the unfolded fabric for an airbag was used.

Thermal Resistance (Sec.) of Fabric=T ₃ −T ₄  [Equation 2]

6) Method of Measuring Strength and Elongation of Yarn

A yarn sample was left in a constant temperature and constant humiditychamber under standard conditions, that is, a temperature of 25° C. anda relative humidity of 65% for 24 hours, and tested by a method of ASTM2256 using a tension tester.

7) Weaving and Coating of Fabric

A plain fabric was woven with a filament yarn to have a yarn density of50 wefts or warps per inch in both of weft and warp directions. A rawfabric was scoured and contracted in aqueous baths which were graduallyset from 50 to 95° C. using a continuous scouring machine, and thentreated at 200° C. for 2 minutes by thermomechanical treatment.Afterward, the fabric was coated with a silicon-based coating agent at aweight of 25 g/m².

8) Airbag Cushion Development Test

A driver airbag (DAB) module was manufactured with a coated fabric foran airbag, and subjected to a static test within several minutes afterbeing left at 85° C. for 4 hours. Here, a pressure of a powder inflatorwas 180 kPa, and when the tearing of the fabric, forming of a pin holeand burning of the fabric were not shown after the development test, itwas evaluated as “Pass.” However, when any one of the tearing of thefabric, forming of a pin hole in a seam and burning of the fabric wasshown, it was evaluated as “Fail.”

MODE FOR INVENTION

Hereinafter, the present invention will be described in detail withrespect to Examples, but the scope of the present invention is notlimited to the following Examples and Comparative Examples.

Example 1

A raw fabric for an airbag was manufactured with a polyethyleneterephthalate yarn having the characteristics listed in Table 1 byplain-weaving using a rapier loom to have a fabric density of 50 weftsor warps per inch in both of weft and warp directions.

Example 2

A raw fabric for an airbag was manufactured with a polyethyleneterephthalate yarn having the characteristics listed in Table 1 by themethod as described in Example 1.

Example 3

A raw fabric for an airbag was manufactured with a polyethyleneterephthalate yarn having the characteristics listed in Table 1 by themethod as described in Example 1.

Comparative Example 1

A raw fabric for an airbag was manufactured with a nylon 66 yarn havingthe characteristics listed in Table 1 by plain-weaving using a rapierloom to have a fabric density of 50 wefts or warps per inch in both ofweft and warp directions.

Comparative Example 2

A raw fabric for an airbag was manufactured with a polyethyleneterephthalate yarn having the characteristics listed in Table 1 by themethod as described in Comparative Example 1.

Comparative Example 3

A raw fabric for an airbag was manufactured with a polyethyleneterephthalate yarn having the characteristics listed in Table 1 by themethod as described in Comparative Example 1.

Example 4

The raw fabric manufactured in Example 1 was scoured and contracted inaqueous baths gradually set from 50 to 95° C. using a continuousscouring machine, and then treated at 200° C. for 2 minutes bythermomechanical treatment. In an uncoated state, the fabric wasmeasured in stiffness, thermal resistance at 350° C. and thermalresistance at 450° C., the results of which are shown in Table 2.

In addition, the manufactured fabric was coated with a silicon-basedcoating agent at a weight of 25 g/m², and thermally treated at 180° C.for 2 minutes. An airbag cushion was made with the thermally-treatedfabric, and subjected to a development test for the airbag cushion. Thetest results and storability in a module are shown in Table 2.

Example 5

The raw fabric manufactured in Example 2 was treated by the methoddescribed in Example 4. Physical properties, results of an airbagcushion development test and storability in a module of the manufacturedfabric are shown in Table 2.

Example 6

The raw fabric manufactured in Example 3 was treated by the methoddescribed in Example 4. Physical properties, results of an airbagcushion development test and storability in a module of the manufacturedfabric are shown in Table 2.

Comparative Example 4

The raw fabric manufactured in Comparative Example 1 was scoured andcontracted in aqueous baths gradually set from 50 to 95° C. using acontinuous scouring machine, and then treated at 200° C. for 2 minutesby thermomechanical treatment. In an uncoated state, the fabric wasmeasured in stiffness, thermal resistance at 350° C. and thermalresistance at 450° C., the results of which are shown in Table 2.

In addition, the manufactured fabric was coated with a silicon-basedcoating agent at a weight of 25 g/m², and thermally treated at 180° C.for 2 minutes. An airbag cushion was made with the thermally-treatedfabric, and subjected to a development test for the airbag cushion. Thetest results and storability in a module are shown in Table 2.

Comparative Example 5

The raw fabric manufactured in Comparative Example 2 was treated by themethod described in Comparative Example 3. Physical properties, resultsof an airbag cushion development test and storability in a module of themanufactured fabric are shown in Table 2.

Comparative Example 6

The raw fabric manufactured in Comparative Example 3 was treated by themethod described in Comparative Example 3. Physical properties, resultsof an airbag cushion development test and storability in a module of themanufactured fabric are shown in Table 2.

TABLE 1 Kind Intrinsic Instantaneous of Viscosity Filament StrengthElongation Thermal Strain Material Yarn (dl/g) size (den) (g/den) (%)Rate (%) Example 1 Polyethylene 500 1.06 2.7 8.4 25.0 2.8 terephthalated/182 f Example 2 Polyethylene 500 1.06 2.7 11.0 18.0 3.5 terephthalated/182 f Example 3 Polyethylene 500 1.06 4.2 9.0 22.6 2.3 terephthalated/120 f Comparative Nylon 66 420 — 6.2 9.7 22.0 1.8 Example 1 d/68 f Comparative Polyethylene 420 1.06 6.2 7.8 14.0 0.4 Example 2terephthalate d/68 f  Comparative Polyethylene 500 1.06 5.2 7.5 12.0 0.6Example 3 terephthalate d/96 f 

TABLE 2 Thermal Thermal Airbag Ability Resis- Resis- Cushion to beStiff- tance at tance at Develop- stored ness of 350° C. 450° C. ment inFabric Fabric (N) (sec.) (sec.) Test for Airbag Example 4  7.4 0.94 0.56Pass Good Example 5  7.6 0.97 0.62 Pass Good Example 6 13.7 0.87 0.50Pass Moderate Comparative Example 4  6.9 0.79 0.46 Pass Good Comparative15.4 0.69 0.39 Fail Bad Example 5 Comparative 17.5 0.73 0.42 Fail BadExample 6

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention as defined bythe appended claims.

1. A fabric for an airbag, comprising: a polyethylene terephthalatefiber manufactured by spinning a polyethylene terephthalate chip havingan intrinsic viscosity of 0.8 to 1.3 dl/g, wherein the fabric for anairbag has a thermal resistance at 350° C. of 0.75 to 1.0 seconds, whichis calculated by the following Equation:Thermal Resistance of Fabric (sec.)=T1−T2  [Equation 1] where T1 is thetime in which a steel rod heated to 350° C. falls from 10 cm above thefabric through the fabric, and T2 is the time in which the same steelrod falls from the same height.
 2. A fabric for an airbag, comprising: apolyethylene terephthalate fiber manufactured by spinning a polyethyleneterephthalate chip having an intrinsic viscosity of 0.8 to 1.3 dl/g,wherein the fabric for an airbag has a thermal resistance at 450° C. of0.45 to 0.65 seconds, which is calculated by the following Equation:Thermal Resistance of Fabric (sec.)=T3−T4  [Equation 1] where T3 is thetime in which a steel rod heated at 450° C. falls from 10 cm above thefabric through the fabric, and T4 is the time in which the same steelrod falls from the same height.
 3. The fabric for an airbag according toclaim 1, wherein the polyethylene terephthalate fiber has aninstantaneous thermal strain rate of 1.0 to 5.0%.
 4. The fabric for anairbag according to claim 1, wherein the fabric for an airbag has astiffness of 5.0 to 15.0 N.
 5. The fabric for an airbag according toclaim 1, wherein the polyethylene terephthalate fiber has a strength of8.0 to 11.0 g/d, and an elongation of 15 to 30% at room temperature. 6.The fabric for an airbag according to claim 1, wherein the polyethyleneterephthalate fiber has a filament size of 4.5 deniers or less.
 7. Thefabric for an airbag according to claim 2, wherein the polyethyleneterephthalate fiber has an instantaneous thermal strain rate of 1.0 to5.0%.
 8. The fabric for an airbag according to claim 2, wherein thefabric for an airbag has a stiffness of 5.0 to 15.0 N.
 9. The fabric foran airbag according to claim 2, wherein the polyethylene terephthalatefiber has a strength of 8.0 to 11.0 g/d, and an elongation of 15 to 30%at room temperature.
 10. The fabric for an airbag according to claim 2,wherein the polyethylene terephthalate fiber has a filament size of 4.5deniers or less.